Tips for using Cisco switches

Cisco is currently the main force in the Exchange industry, and its products are doing very well in the market. Here we mainly analyze some usage skills of Cisco switches. As a network manager, it is inevitable to debug switches frequently. The core backbone switches in Xiangzi are mainly Cisco switches. In the process of debugging and maintaining Cisco switches, Xiangzi may encounter some headaches. Fortunately, after a period of system learning, these problems have been solved one by one. In fact, understanding these methods is very helpful for improving the efficiency of debugging vswitches. Here, we will introduce some accumulated experiences for your reference.

I. How to Prevent the system information from interfering with the command input?

I believe many network administrators and friends have encountered this problem: when debugging a Cisco switch through the CONSOLE port connected to the switch through a serial port (except for the first time configuring the switch, most of them are due to a switch failure and cannot be logged on through the network port). This is often the case when 100,000 is in a rush, but the more urgent it is, the more difficult it is to find a command than to log on to the sky, this is because some system prompts will pop up from time to time (or constantly) on the configuration interface opened by the Super Terminal. At this time, the command input will be completely disrupted, that is to say, you cannot enter a complete string of commands in one line. At that time, it was a test of the psychological quality of the network administrator and the keyboard-based fingering method. It can be described by typing commands with your eyes closed, after the command is completed, it is expected that the error will be eliminated and so many error messages will not be displayed (of course, it will not succeed in ). In fact, there is a way to deal with these constantly changing information. When we log on through the CONSOLE port, we only need to type 3550 # conf t.

In this way, you can effectively avoid the interference caused by commands repeatedly popped up by console messages when you enter commands. In fact, logon through the network port will also be affected by system information, but this situation does not appear in the Cisco switch by default, but it can be implemented with only one command: 3550 # terminal monitor. In order to experience the actual effect, we can open two DOS windows on our microcomputer and log on to the same Cisco switch via TELNET, one for monitoring, in addition, perform the following operations: for example, we can execute one port shutdown and then no shutdown, in this case, the system information is disturbed when you want to enter the command in the first window, as shown in the following figure: 3550 (config )#.

In fact, I want to type inter fa0/4, but this command is drowned in the system prompt information. If you want to solve the problem, just type the following command: 3550 # conf t; Enter configuration commands, one per line. End with CNTL/Z. TELNET logon and CONSOLE logon. If you want to prevent the input command from being disturbed by the prompt information of the switch, you can solve the problem in the same way.

2. Do not allow the vswitch to try to use the DNS server to resolve the Host Name

What does this mean? When debugging a switch, we will inevitably enter an incorrect command, for example, if we type one more letter or one less letter, I thought the switch would prompt this command error, but a strange thing happened at this time. The system didn't prompt us for a command error, but made a connection to it (that is, the command was executed the same ), 3550 # beijing.

That is to say, the Cisco switch considers the incorrect command as the host name and tries to resolve it by querying the DNS server. If the DNS server is set on the switch, the progress will be faster. If there is no DNS server, the progress will be slow. How can we avoid this situation? Enter the following command: 3550 # conf t. After the preceding commands are executed, when an incorrect command is entered, the Cisco switch will not perform unnecessary connections for a long time.

3. quick understanding of port disconnections in vswitches

As a network administrator, when we access a new service on a vswitch, we always need to find an idle port on the Cisco switch and configure necessary services, connect the network cable, but when there are many cables on the switch, with the naked eye, it is difficult to accurately identify idle ports at once (if an error is accidentally pulled, the Network may fail). Therefore, we used to log on to the switch, run the following command: 3550 # show inter. At this time, the switch will display the details of each port in sequence, including the port disconnection, but it is still too slow. In fact, there are more direct commands, as shown below:

3550 # show ip interface brief
Interface IP-Address OK? Method Status Protocol
Vlan1 unassigned yes nvram administratively down
Vlan2 172.19.96.1 yes nvram up
FastEthernet0/1 unassigned YES unset up
FastEthernet0/2 unassigned YES unset up

As shown in the preceding figure, the port disconnection status on the Cisco switch can be obtained directly, but the VLAN information is also included. If we only want to know the disconnection status of the physical port, run the following command:

3550 # show ip interface brief | I Fast
FastEthernet0/1 unassigned YES unset up
FastEthernet0/2 unassigned YES unset up
FastEthernet0/3 unassigned YES unset up

The above three points are some of the experience accumulated by Xiangzi in learning to use Cisco switches. I hope to provide some reference to my friends and open up the fog of faults to identify the real causes of network faults.